A method and an apparatus for distributing the flux density of an input light flow are known from U.S. Pat. No. 4,911,711. Here, an input light flow having a Gaussian distribution of its flux density over its cross-section is split-up into three light flows by means of two fully reflecting optical surfaces and along two splitting planes running in parallel to the optical axis of the input light flow and in parallel to each other splitting planes, each of the fully reflecting optical surfaces deflecting the light flow by a 90° whereas the central light flow passes between these two fully-reflection optical surfaces without deflection. The two deflected light flows are then coaxially superimposed with the not deflected light flow by means of two beam dividers. At the partially reflecting optical surface of each beam divider, the transmitted fraction of the flux density of the non-deflected light flow is superimposed with the reflected fraction of the flux density of the deflected light flow. The output light flow thus comprises partial flows of all three light flows. Prior to their combination with the not deflected light flow each of the deflected light flows is reflected four times, so that the deflected light flows are finally only shifted sideways, but are not inverted with regard to the not deflected light flow. By means of coaxially superimposing the light flows, the flux density of the input light flow is re-distributed in a sense of homogenizing the flux density distribution of the output light flow. The light flow loss caused by execution of this known method is comparatively high, as at each beam divider employed for the integration of two light flows some partial flows of both mentioned above light flows are lost. Actually, these are the flux density fractions of the not deflected light flow reflected by the partially reflecting optical surface, and the transmitted flux density fractions of the deflected light flows.
From German Patent DE 197 24 060 C2 both a method and an apparatus for distributing the flux density of an input light flow are known, by which it is intended to homogenize a Gaussian distribution of the flux density of a laser beam. To this end, the input light flow of the laser beam is split by a beam divider into two partial flows each of which comprises a flux density fraction from the total cross-sectional area of the input light flow. The partial flow reflected by the partially reflecting optical surface of the beam divider is converted by means of reflective and also refractive optical elements, as appropriate: at first, it is split-up into two light flows, next, each light flow is inverted by reflection, and then the inverted light flows are assembled again side-by-side. The reflected partial flow converted in this way and the not reflected partial flow are superimposed at the rear side of the same beam divider which divided the input light flow into the partial flows. As the converted partial flow exhibits a minimum in the area of the beam center, whereas the transmitted partial flow exhibits the Gaussian distribution of the flux density with a maximum in the area of the beam center, the superposition results in an output light flow homogenized regarding its flux density distribution. However, the loss of light flow is rather large also in this case because the beam divider, superimposing the converted partial flow with the transmitted partial flow, lets a flux density fraction of the converted partial flow pass through, which comes out of use.
A beam dividing apparatus which splits-up an input light flow into a number of light flows and which aligns these light flows in parallel to each other by means of partially reflecting and fully reflecting optical surfaces on transparent, plane-parallel plates arranged in parallel to each other to produce an output light flow having a broadened cross-section is known from German Patent DE 36 45 001 C2.
A beam splitter assembly comprising a transparent plane-parallel plate provided with partially reflecting and fully reflecting optical surfaces in different partial areas is also known from the German Patent Application DE 199 58 555 A1.
A beam divider whose partially reflecting surface comprises an array of a plurality of fully reflecting and fully transparent micro areas arranged side-by-side is known from Gottfried Schröder, Technische Optik, 8. Edition, Vogel Buchverlag, p. 43.
It is known from Y. Kawamura et al.: “A simple optical device for generating square flat-top intensity irradiation from a Gaussian laser beam”, Optics Communications, Vol. 48, No. 1, p. 44 ff. to use a prism system for splitting-up an input light flow having a Gaussian distribution of the flux density over its cross-section into four light flows and for simultaneously aligning it in such a way that the cross-sections of the light flows are overlapping. There, where the cross-sections of the light flows are overlapping, the flux density distribution over the integral cross-section is comparatively homogeneous. The light flows, which are combined into the output light flow, are, however, not aligned coaxially here but in diverse directions. Thus, the combined output light flow is strongly divergent, and it exhibits no homogenization of its flux density except of the area in which the cross-sections of the light flows actually overlap.
Thus, there is a need for a method and an apparatus for distributing the flux density of an input light flow, in which losses of the light flow are considerable reduced, and in which a desired distribution of the flux density is nevertheless achieved not only in the area of a single plane, and in which the divergence of the output light flow is not increased to a relevant extent.